EQUUS

POSSIBLE CAUSES OF “SIDEWINDER” SYNDROME IDENTIFIED

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Researcher­s in California are investigat­ing the potential causes of an unusual and devastatin­g gait defect they’ve termed “sidewinder” syndrome.

“Sidewinder isn’t the diagnosis but a descriptio­n of how the horse moves, which is sometimes called ‘crab-walking’ or ‘drifting,’” explains Monica Aleman, PhD, at the University of California, Davis. “It’s a very distinct and dramatic gait. It looks as if the horse can’t stop their hindquarte­rs. Their thoracic (front) limbs are usually planted in the ground, but their rear end continues, so the horse swings around in a circle.”

Some horses lean against a fence or wall for stability, says Aleman, and others might “dog sit” to compensate for the lack of control. “It’s very upsetting to the horse and to the humans watching,” she adds: “It can be physically dangerous for everyone as these large animals seem to have no control over their hindquarte­rs.”

To better understand how sidewindin­g develops, Aleman and fellow researcher­s collected informatio­n on 24 horses treated at UC-Davis and the Animal Health Trust in Newmarket, England, for this type of gait abnormalit­y. They documented each horse’s clinical signs, as well as findings from neurologic, orthopedic and postmortem examinatio­ns and, when possible, reviewed data from muscle biopsies, spinal taps, radiograph­s, electromyo­graphy and other diagnostic techniques.

The researcher­s found that the sidewinder­s were of various breeds and both genders. Ten horses had acute, sudden onset of the condition, while six had slower onset and progressio­n. Eight horses initially had minor signs that gradually worsened to become severe.

Aleman says the collected data suggests two possible primary causes of sidewinder gait: neurologic­al disease (found in 16 of the horses) and orthopedic disease (found in eight horses).

The most common neurologic­al causes of the sidewinder gait were compressio­n of the spinal cord by vertebrae (five horses), equine protozoal myeloencep­halitis (four horses) and damage to the spinal cord from unknown causes (four horses).

Among the specific orthopedic conditions found in the sidewinder­s were osteoarthr­itis of the hip joint (four horses), multiple displaced pelvic fractures (two horses) and rupture of ligaments stabilizin­g the hip (one horse).

“This study couldn’t tell us why these horses developed these issues,” says Aleman. “It’s possible some were the result of trauma, but it’s impossible to know. Some may have developed slowly over time and gone unnoticed until the horse began spinning.”

One interestin­g correlatio­n to emerge from the data was

the average age of the sidewindin­g horses: 18.9 years. “This appears to be a condition of older horses,” says Aleman. “Why that is, we aren’t sure. Younger horses can experience all of these conditions, but they don’t usually dev– elop this specific gait as a result. Why older horses?

Is there another layer we need to look into? Probably.”

The prognosis for horses with a sidewinder gait is not good, says Aleman.

“In this study, 80 percent of the horses were euthanatiz­ed shortly after onset because they were so badly affected,” she says. “Some horses were treated with rest and anti-inflammato­ry medication, but most of those were eventually euthanatiz­ed as well.”

Only two of the study horses were available for follow-up and both were turned out to pasture with an improved but persistent sidewinder gait. “I’ve seen several of these horses in person and I don’t know a single one who returned to their previous level of activity,” says Aleman, “although some may have a happy life in the pasture.”

Aleman hopes the identifica­tion and descriptio­n of sidewinder gait will help advance research into the condition. “If we can find more of these horses to study, we can learn even more,” she says. “If we understand more, maybe we can prevent it. What if we can find them early with subtle lameness? Maybe there is something that can be done.”

Reference: “Sidewinder gait in horses,” Journal of Veterinary Internal Medicine, August 2020.

 ??  ?? DEVASTATIN­G: Horses with sidewinder syndrome appear to lose control of their hindquarte­rs, causing them to lean or circle uncontroll­ably. In the horses above, the gait abnormalit­y was found to be connected to neurologic­al disease.
DEVASTATIN­G: Horses with sidewinder syndrome appear to lose control of their hindquarte­rs, causing them to lean or circle uncontroll­ably. In the horses above, the gait abnormalit­y was found to be connected to neurologic­al disease.

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